1. Field
The present invention relates to a structure of an engine of a projector used in projecting an image on a screen in various kinds of presentation and at home.
2. Description of the Related Art
A related art is disclosed, in which an engine of a projector used for presentations is formed by an optical unit, the optical unit modulates a light flux ejected from a light source device according to image information so as to form an optical image, a projected image is formed on a screen through a projector lens, and when a casing is made of synthetic resin in a projector, a light source driving circuit needs an electronic shielding member to become an EMI (electromagnetic interference) generating source (refer to JP-A-2004-205714). Further, a method in which a shield plate shielding the EMI generating source is attached to a cover member for the exchange of the light source lamp by an attaching screw so as to prevent a detachment of the shield plate is described in the document JP-A-2004-205714.
In another related art, in order to shield electromagnetic waves, which are radiated from a flat cables which connect the drive circuit block of a liquid crystal projector with a liquid crystal panel, a metal sheet is formed by punching holes in an aluminum thin film or the like by a metal mold, and the metal sheet is inserted into an opening of a shield case and fixed by threading in an attaching hole of a drive circuit block (refer to JP-A-9-232785).
In another related art, a shield member made of metal sheet is accommodated in an outer case made of resin of a projector (refer to JP-A-2003-017865).
FIG. 4 is a side view schematically showing an external constitution of the projector engine section which corresponds to a projector engine section described in the document JP-A-2004-205714, and FIG. 5 shows a casing frame 1, a circuit board 3 and a heat sink 4 of the engine section.
As shown in FIG. 4, a cover 2 made of sheet metal disposed in an upper portion of the casing frame 1 constitutes a hollow housing, various kinds of optical parts are built in the housing. A projector lens 12 is provided in front of the housing, and the circuit board 3 having a digital mirror device control circuit attached thereon and the heat sink 4 are disposed in this order behind the housing. An engine section 100 functions as an optical unit, that is, exerts in projecting an optical image formed by modulating light flux according to image information through a projector lens. In this respect, to prevent deterioration of video restoring performance due to a leakage of light from the engine section, the casing frame 1 or the cover 2 also prevents the light from leaking by sealing the engine section 100. At the same time, the heat sink 4 dissipates the heat generated in the sealed engine section 100 so as to prevent a heat generation due to the fullness of heat in the engine section 100. In the meantime, as shown in FIG. 5, an upper portion of the casing frame 1 is open, a mouth edge portion 14 of an aperture 13 thereof is provided with a projection 15 and a screw hole 16 on the right and left side. The cover 2 shown in FIG. 4 is attached on the mouth edge portion 14 of the aperture 13 by using the projection 15 and the screw hole 16.
It is assured that electromagnetic interference (EMI) is generated as electromagnetic noise coming from the circuit board 3 is radiated through a fin of the heat sink 4, in the engine section 100 having the above-described structure. Accordingly, measures (EMI-prevention) have been taken to prevent the electromagnetic interference.
FIG. 6 is a cross-sectional view showing a conventional EMI-prevention. FIG. 7 is a perspective view schematically showing a rod-shaped gasket 5 used for an EMI-prevention.
The rode-shaped gasket 5 of FIG. 7 used in the conventional EMI-prevention is formed by wrapping and insulating a core 51 having elasticity with a mesh material (metallic mesh) 52 having conductivity and flexibility. In the EMI-prevention, as the rod-shaped gasket 5 is inserted into a space between the circuit board 3 and the heat sink 4 opposite to each other, the rod-shaped gasket 5 is held in the space by the elasticity of the rod-shaped gasket 5. Measures has been taken in which the rod-shaped gasket 5 is attached to the circuit board 3 and the heat sink 4 by using Double-sided adhesive tape. In addition, as shown in FIG. 6, the tip of the cover 2 is superimposed on the mouth edge portion 14 of the casing frame 1 so as to combined with the casing frame 1 by the attaching screw 17 that is screwed into a screw hole 16 of the mouth edge portion 14.
However, according to the conventional EMI-prevention described with reference to FIG. 6, it is known that an impact applied on the engine section 100 during assembly processing or vibrations that can occur in other circumstances can cause the rod-shaped gasket 5, serving as the EMI-prevention, inserted into the space between the circuit board 3 and the head sink 4 to be dislocated or fall off the space, so that electromagnetic interference suppressing performance becomes deteriorated. This setback can be seen as well when the rod-shaped gasket 5 is attached to the circuit board 3 and the heat sink 4 by using double-sided adhesive tape.